Field of the Invention
The present invention relates to an automatic transmission for a vehicle.
Description of Related Art
In the field of an automatic transmission, multiplicity of shift-stages is a useful technology for enhancement of fuel consumption and drivability of a vehicle. Recent increases in oil prices are triggering stiff competition among auto-makers in enhancing fuel consumption of a vehicle.
In this sense, research on an engine has been undertaken to achieve weight reduction and to enhance fuel consumption by so-called downsizing and research on an automatic transmission has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages.
In order to achieve more shift stages for an automatic transmission, the number of parts, especially the number of planetary gear sets, is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency.
Therefore, development of a planetary gear train capable of achieving maximum efficiency by minimum number of parts is substantially beneficial for maximizing improvement of fuel consumption by multiple shift-stages of an automatic transmission.
In this respect, an eight-speed automatic transmission has been recently introduced, and a planetary gear train for an automatic transmission enabling more shift stages is under investigation.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.